48 ESSENTIALS OF BACTERIOLOGY. 



the moist chamber, when they of their own weight fall aside, 

 the cut surface uppermost. They are then ready for inoculation. 



FIG. 21. 



Method of slicing potato. (After Woodhead and Hare.) 



Esmarch's Cubes. The potato is first well cleaned and peeled. 

 It is then cut in cubes inch in size. 



These are placed, each in a little glass dish or tray and then 

 in steam-chest for hour, after which they are ready for inocu- 

 lation (the dishes first having been sterilized in hot-air oven). 



Test-tube Potatoes. Cones are cut out of the peeled potato 

 and placed in test-tubes, which can then be plugged and easily 

 preserved. 



Manner of Inoculation. With a platinum rod or a spatula 

 (sterilized) the material is spread out upon one of the slices, 

 keeping free of the edges. The growth on this first or original 

 potato will be quite luxuriant, and the individual colonies often 

 difficult to recognize, therefore dilutions are made. (Fig. 22.) 



From the original or first slice, a small portion including some 

 of the meat of the potato is spread out upon the surface of a 

 second slice, which is first dilution. From this likewise a small 

 bit is taken and spread on a third slice or second dilution, and 

 here usually the colonies will be sparsely enough settled to study 

 them in their individuality. 



This is the principle carried on in all the cultivations. It is 

 a physical analysis. 



